Japanese Utility Model Examined Publication No. Sho44-18178 (hereinafter referred to as Patent Document 1) discloses a ferrite antenna. This ferrite antenna has a bar-shaped ferrite core, a coil bobbin into which the ferrite core is inserted, a main coil wound around the coil bobbin, and a small coil provided on each side of the main coil. In this ferrite antenna, the main coil is moved in a length direction of the ferrite core to cause a change in inductance, making it possible to perform tracking adjustment.
However, in the conventional ferrite antenna, the electrical connection between the small coils and the main coil is effected by using windings forming these coils as they are.
Thus, in a case in which the main coil is moved with a view to setting the reactance value of the ferrite antenna to a desired value, when the main coil is released, the main coil is pulled by the windings connecting the small coils and the main coil, resulting in positional deviation of the main coil. If the main coil is fixed in position by resin, a tape or the like while retaining it by hand, etc., the main coil is likely to be shifted during curing of the resin, or the adhesive force of the tape is likely to be reduced, resulting in positional deviation of the main coil. As a result, the completed product is likely to involve variation in reactance value. Further, in the case in which an attempt is made to fix the main coil at a desired position with resin, the next operation cannot be performed until the resin has been dried and cured, resulting in a rather long assembly time.
To suppress such positional deviation of the main coil, it might be possible to increase the length of the windings connecting the small coils and the main coil, attaining a length providing some room with respect to the adjustment range of the main coil. However, when the length of the windings connecting the small coils and the main coil is increased, the wiring may be shaken due to vibration or the like applied to the ferrite antenna, and a fatal problem, such as a breaking of wire, is likely to occur. Further, due to the shaking of the windings connecting the small coils and the main coil, it is rather difficult to stabilize the reactance value.
The present inventor has conducted careful study to solve the above problems before completing the present invention.
An object of the present invention is to obtain an antenna coil and an antenna device which allow easy positional adjustment of the winding sand which is relatively free from positional deviation of the windings after the adjustment.